In recent years, ITS systems have been developed that are systems for networking humans, roads, and vehicles through information using information communication technology. There is especially a demand for a traffic information system that reduces traffic congestion and accidents and realizes safe and efficient driving by guiding the traveling of vehicles in accordance with traffic conditions on roads. In such a traffic information system, it is useful to perform definition and detection of a vehicle group, selection of a representative vehicle or the like as required, and technology for vehicle group management is required.
There are known vehicle travel guiding apparatuses that are equipped with vehicle group identifying means for judging whether a vehicle group has been formed or not based on the position and speed of vehicles traveling on a road (see Japanese Patent Laid-Open No. 2002-373395, for instance). Also, vehicle group formation systems are known in which a representative vehicle of a vehicle group communicates with a base station and delivers a request relating formation or dissolution of a vehicle group and the like received from the base station to other vehicles (see Japanese Patent Laid-Open No. 2002-198886, for instance).
A known technique using a vehicle travel guiding apparatus needs detection of position and/or speed of vehicles for identifying a vehicle group and requires installation of a detector for that purpose in each roadside device. Also, in the aforementioned vehicle group formation system, significant burden is placed on a network of the vehicle group formation system in individual phases, such as formation and dissolution of a vehicle group, because vehicle group management is carried entirely out at a high level of the network.